Method of burning pulverized fuel



Patented Dec. 28, 1937- PATENT, OFFICE METHOD or BURNING ruLvcmzEn FUEL Benjamin Graemiger, Zollikon, Swltzerlandfassignor to Hephaest A.-G.

fiir motorische Krafterzcugung, Zurich, Switzerland, a corporation of Switzerland Application June 22, 1934, Serial No. 731,822 In Switzerland June 28, 1933 5 Claims.

This invention relates to a method of firing a combustion chamber in which a pressure of at least 0.2 kilogram per square centimeter is maintained, and in which pulverized fuel is employed.

The maintaining of a pressure in combustion chambers substantially above atmospheric pressure is of great importance, particularly for steam boilers, because the increased pressure and.

greater fuel gas speed permits decrease in the dimensions of the combustion chamber and of the heating surfaces, and permits more rapid and more intensive combustion and heat interchange.

vided condition to the combustion chamber. Pulverizing the fuel by ordinary pulverization, and at atmospheric pressure, and then delivering the fuel to the chamber'under, superatmospheric pressure, 'has not proved satisfactory or reliable.

The variations in the amount of moisture retained in the fuel, thespeed at which the change in pressure occurs, and the difficulties involved in V delivering the solid fuel from atmospheric pressure to the higher pressure, precludes proper proportioning, uniform mixing, etc. These difficulties have'been ovrcome by the present invention, in which the fuel is pulverized under a pressure sumciently higher than that employed in the combustion chamber to permit of the delivery of the resulting fine fuel in an air or other gas stream directly into the combustion chamber, with the proper proportioning, and by the uniform mixing with the combustion supporting gas.

As the coal or other solid fuel is pulverized under the pressure higher than that in the combustion chamber, the freshly prepared dust is immediately conveyed by the transferring air stream, and does not have any opportunity of depositing, and is delivered at the rate at which it is being pulverized. The dust remains suspended in the transferring air stream, and therefore is in properly dispersed condition for proper burning the instant it reaches the combustion chamber. The regulating thus becomes very simple, and it is not necessary to increase. the pressure on the fuel after it has been pulverized. as is necessary where the fuel is pulverized under a lower pressure than that-existing in the combustion chamber.

The pulverizer is preferably of the so-called pneumatic or impact type, where the pulverizetion is eflected by means of an air jet, and therefore the pressure in the pulverizer may be readily varied by control of the blower or other means employed for delivering the jet under pressure to the pulverizer, and the pressure in the pulverizer may be varied in accordance with the pressure which it is desired to maintain in the combustion chamber. The supply of raw fuel to the pulverizer operating under pressure is effected advantageusly by interposing at least two containers which are filled and used alternately and are thus maintained free from pressure during the filling period and are subjected during the use to the pressure prevailing in the pulverizer.

* The raw fuel may, however, also be forced into a container by a continuously operating conveying device, the container being subjected, at least approximately, to the pressure of the pulverizer and the raw fuel being supplied to the pulverizer at the ratio of its comsumption. The raw material may also be supplied directly to the pulverizer and subjected to pressure, by a. continuously operating conveyor device. It will be understood that the conveyor devices may be subjected to the action of any suitable regulating device. The method is particularly advantageous and simple when the pulverized fuel is produced in a pneumatic pulverizer by the work of expansion of a compressed gas. In this connection there is used, as a rule, at least a portion 'of the necessary combustion air for the operation of the pulverizer. a

In the accompanying drawing: I

Fig. I shows a diagrammatic illustration of the method according to the invention in the case of alternately filled intermediate containersin combination with a pneumatic pulverizer.

Fig. 2 shows a diagrammatic illustration of the method in the case of an intermediate container subjected topressure and charged by a continuously operating conveyor device, also in combination with a pneumatic pulverizer.

In Fig. 1, i indicates a combustion chamber, and 2 a rotary multi-stage compressor. This draws in fresh air at 3. A portion of the compressed air is blown from the compressor at an intermediate stage and at an intermediate pressure and is forced through the pipe 5 as combuspipe 5, is forced through the pipe 4 and conducted pressed air, at a higher pressure than that in the 9. The fuel is pulverized by relative impinging and friction between the separate fuel particles and by impact with the body 9. The fuel-air mixture enters the combustion chamber I through the pipe l0. The air which performs the pulverization thus forms a portion of the combustion air. The air forced from the compressor through pipe 4 is compressed to a sufficiently higher degree than the general combustion air forced from the' compressor through pipe 5, to perform the pulverizing operation. The two closed fuel hoppers Ii are connected to the impact pulverizing device i by the pipes l2. The charging of the containers is obtained for example by a pneumatic device, notshown, in such a manner that a vacuum is produced by a blower connected to the pipe l3 so that raw fuel is supplied to the containers it through the pipes It from a source of supply not shown. During the charging of one of the containers the valves l5, lB'of that container are opened whilst the valves 18 and 20 of that container are closed. After charging l and it are closed, and i8 and 2!] opened whereby the pressure existing in the pulverizing device is first transferred through the pipe IT to the container. The fuel then flows through the pipe it into the reservoir at the lower end of the pipe which forms part of the pulverizing device. The use of pipe Hi to quickly equalize pressures between hopper liand pulverizer l is advantageous, since it substantially prevents gas fiow up pipe l2 and consequent delay in establishing a balanced pressure. This arrangement also eliminates the danger of packing or agglomerating the fine moist coal in pipe IE or the formation of bridges therein which might cause stoppage of the flow of coal. The pipe coil is indicates how the air flowing to the pulverizing device may be heated.

In Fig. 2, 26 indicates a pneumatic pulverizing device into which compressed gas (for example heated combustion air) is supplied by a pipe 22 and from which the combustible mixture of air and pulverized coai is conducted by the pipe 23 to the combustion chamber, not shown. The pulverizing device is connected by the pipe 25 to a container 24% which is subjected at least substantially to the same pressure as exists in the pulverizing device. By means of the conveyor worm 2T, driven by a motor 28,'fuel is fed continuously from a container 28, whilst overcoming the static counterpressure, into the container 25. It is preferable not to extend the worm'right up to the'discharge point so as to obtain a more effective packing (stumng box efi'ect).

Instead of air, waste gas, for example, maybe used for the operation of the pulverizing device.

This may be of advantage when a fuel of high larly at comparatively high temperatures, in order that the process of. pulverization is not effected with air, but with a neutral gas. Instead of heating the air flowing through the pipe 4 by pipe coil l9, the same purpose may be served in various other ways. There may also be used waste gases derived, for example, from combustion engines, which gases may possibly be withdrawn from the engines at a pressure, obviating the use of a separate compressor. The method is applicable equally to combustion under constant pressure or according to the exploding principle.

What I claim is:-,

1. The method which includes compressing a gas, delivering a part of said gas to a combustion zone, maintaining in said combustion zone a pressure substantially above that of the atmosphere, further compressing the remainder of said gas to a higher pressure, expanding said last mentioned gas to form a jet at a pressure above that of said combustion zone, delivering a fuel to said jet, pulverizing said fuel by impingement, and conducting said expanded gas from said jet and the pulverized fuel to said combustion zone.

2. The method of pulverizing and burning solid fuel, which comprises maintaining a super-atmos pheric pressure of not less than 0.2 kilogram per square centimeter in a combustion chamber, compressing air to a higher pressure, expanding said air through a nozzle to form a jet at a pressure higher than that maintained in the combustion chamber, introducing fuel into the jet of expanding air, pulverizing said fuel by impingement, and delivering the expanded air and pulverized fuel into the combustion chamber.

3. The method of pulverizing and burning solid fuel, which comprises maintaining a super-atmospheric pressure in a combustion chamber, compressing air, expanding the air to form a jet at a. pressure slightly greater than that maintained in the combustion chamber, delivering solid fuel to the gas after expanding, pulverizing the fuel by impingement, conveying the pulverized fuel to said combustion chamber by the flow of said expanded gas from the point of pulverizing to-the point of burning, and burning the pulverized fuel in said combustion chamber to thereby produce compressed combustion gas.

e. The method which includes compressing a combustion supporting gas and delivering it to a combustion zone, maintaining in said combustion zone a pressure substantially above that of the atmosphere, compressing a gas to a pressure higher than that of the first mentioned gas, expending said last mentioned gas to form a jet at a pressure above that of the combustion zone, delivering a fuel to said jet, pulverizing said fuel by impingement, and conducting said expanded gas from said jet and the pulverized fuel to said combustion zone.

5. The method which includes pulverizing c'oal in the presence of a "gas under a pressure substantially above that of 'the atmosphere, and blowing the pulverized coal into a combustion chamber maintained at a pressure substantially above that of the atmosphere but sumciently bedirect propulsion of the pulverized coal by the gas flowing from the pulverizer into the combustion chamber.

BENJAMIN GRAEMIGER.

' low that maintained in the pulverizer -to permit 

